A great variety of tools have been devised for the purpose of recovering articles dropped or broken off in oil well operations. Such lost objects are usually referred to as "fish" and the retrieval tool as a "fishing tool."
In U.S. pat. No. 5,242,201, granted to the applicant of the present invention, there is disclosed in one embodiment one form of a fishing tool known as a fishing spear. With reference to FIG. 13, the fishing spear A of the '201 patent includes an upper sub 10' having a shoulder 14' against which spring 16' bears. The opposite end of spring 16' bears on shoulder 18' formed on collet ring 20'. Collet ring 20' is mounted for translatable movement on mandrel 12'. Collet ring 20' has an outer cover 22' fixedly attached thereto. A variable volume cavity 34' is formed between collet ring 20' and mandrel 12'.
Collet ring 20' includes a plurality of collet fingers 36' with each collet finger 36' having a collet head 38' at the end thereof. Collet heads 38' are shown abutting the lower surface of mandrel 12'. More particularly, collet heads 38' are positioned against large diameter portion 40' of mandrel 12' immediately above shoulder 46'.
Fish 48' has an internal groove 50'. The outside diameter of collet heads 38', when seated against the large diameter portion 40' of mandrel 12', is larger than opening 54' of fish 48'. When spear A is used to retrieve fish 48', the end of mandrel 12' is inserted into fish 48' as shown in FIG. 13. As further seen in FIG. 14, further displacement of the end of mandrel 12' into fish 48' causes collet heads 38' to come into contact with fish 48', causing the upward displacement of collet heads 38' as the end of mandrel 12' continues to enter fish 48'. As collet heads 38' are pushed upwardly along mandrel 12' due to the engagement with fish 48', spring 16' is compressed and variable volume cavity 34' increases in volume.
A lower lip 47' is formed on the bottom of upper sub 10'. Spring 16' surrounds lower lip 46'. The expansion of variable volume cavity 34', i.e., the upward movement of collet 20', is limited by the full compression of coil spring 16'. During the upward movement of collet 20' along mandrel 12', collet heads 38' first slide along enlarged diameter portion 40' of mandrel 12', and then up inclined ramp 42'. Collet heads 38' are cammed towards reduced diameter portion 44' by fish 48' after sliding up inclined ramp 42'. Collet 20' continues to slide upwardly along mandrel 12' until spring 16' is fully compressed. A circumferential gap 24' is created between fingers 36' and cover 22'. At this point, the external diameter of collet heads 38' is less than opening 54' of fish 48', so further axial movement of spear A into fish 48' causes collet heads 38'to enter fish 48'.
When collet heads 38' are positioned within fish 48' (not shown in FIGS. 13 and 14), and more particularly when collet heads 38' are adjacent internal groove 50' in fish 48', the direction of mandrel movement is reversed. This causes collet heads 38' to slide down inclined ramp 42'. As they do so, collet heads 38' are pushed radially outwardly into internal groove 50' of fish 48'. Mandrel 12' is further raised until collet heads 38' are again positioned immediately above lower shoulder 46' of mandrel 12'. Collet heads 38' are then locked into internal groove 50' and fish 48' can be raised.
The fishing spear of the '201 patent requires an initial collision between collet heads 38' and fish 48' in order to push collet heads 38' up large diameter portion 40' and along inclined surface 42' on mandrel 12' to the point where their diameter is reduced far enough so that they can enter fish 48'. The collet ring 20' of the '201 patent is generally a relatively thin tubular body, having essentially cantilevered collet fingers 36' extending therefrom. Due to their relative thinness, collet fingers 36' inherently have low buckling strength. The repeated collisions and buckling forces sustained by collet ring 20' weakens fingers 36', sometimes to the point where fingers 36' rupture, leaving broken collet fingers 36' and collet heads 36' in the well casing.
Further, well casings are generally rather harsh environments. Debris such as sand, carbolite and scale accumulate within and on the sides of the well casing. In addition, when using wireline units, segments of wire become torn from the unit and are left in the well casing. Moreover, segments of the well casing are often attached with casing collars, which can create irregularities in the internal diameter of a well casing. Consequently, when fishing in a well casing, the tool collides with the irregularity. Still further yet, the well casing itself sometimes is not perfectly axially aligned, creating further irregularities which must be traversed by the fishing tool. These and numerous other general characteristics of well casings create hazards for fishing tools.
The '201 fishing spear design includes external operating mechanisms, including collet ring 20', cover 22' and spring 16', which reciprocate to contribute to the retraction and expansion of the collet heads 38'. Spring 16', cover 22' and shoulder 46' are exposed to the inside of the well casing. Consequently, when traveling down the well casing to engage a fish and when being pulled from well casing after the fish has been secured, sand, carbolite, scale and other debris tends to accumulate in the toroidal space defined on the outside by spring 16', on the inside by mandrel 12', at the top by lip 47' and at the bottom by shoulder 18'. Not only does the presence of these foreign substances cause spring 16' to wear, they also impact on the performance of the fishing tool by, e.g., preventing complete compression of the spring during expansion of cavity 34'.
In addition, after collet heads 38' ride up inclined surface 42' on mandrel 12' and become positioned against reduced diameter portion 44', circumferential gap 24' (FIG. 14) opens. Debris within the well casing often collects within circumferential gap 24'. The debris in gap 24' tends to wedge collet fingers 36' and collet heads 38' into the inactive position, i.e., against reduced diameter portion 44' of mandrel 12'. Under normal operations when mandrel 12' is raised after it has been inserted into fish 48', collet heads 38' ride along inclined surface 42'. Any debris within gap 24', however, tends to prevent collet fingers 36' from returning flush with casing 22'. If the collet heads 38' are forcefully returned to the active position, i.e., against enlarged diameter portion 40', collet fingers 36' may be caused to bend slightly about a point defined by the debris. In an extreme case, debris accumulates in gap 24' to the extent that collet heads 38' are prevented from sliding down inclined surface 42' and against the enlarged diameter portion 40' of mandrel 12'. In other words, the tool jams.
Still further, since the '201 fishing spear is mechanically actuated, collet heads 38' may begin sliding up mandrel 12' without encountering a fish. This could occur, for instance, if the tool traverses a misaligned casing collar. Casing collars are generally provided every 30-50 feet in the well casing. With well casings often exceeding 10,000 feet in depth, collisions between fish and misaligned casing collars are not uncommon. Thus, if any of the casing collars are out of alignment, the '201 fishing spear abuts against them, causing premature actuation of the fishing spear. While the '201 spear often successfully passes misaligned collars, gap 24' is opened to debris.
Another fishing tool disclosed in the '201 patent is depicted in FIGS. 15-18. This form a fishing tool is referred to in the industry as an overshot or an external pulling tool. For convenience, reference numerals in FIGS. 13-14 are used in FIGS. 15-18 to depict similar elements. With reference to FIG. 15, overshot A includes an upper sub 10' having a shoulder 14' against which spring 16' bears. The opposite end of spring 16' bears on shoulder 18' formed on collet ring 20'. Collet ring 20' is mounted for translatable movement on mandrel 12'. An outer cover 22' is fixedly attached to upper sub 10'. Outer cover 22' includes at the lower end thereof a lower shoulder 46', vertical small internal diameter surface 40', inclined surface 42' and vertical large diameter surface 44'. A variable volume cavity 34' is formed between collet ring 20' and mandrel 12'.
Collet ring 20' includes a plurality of collet fingers 36' with each collet finger 36' having a collet head 38' at the end thereof. Collet heads 38' rest on lower shoulder 46' of outer cover 22'. Fish 48' has an external groove 50'. The inside diameter of collet heads 38', when seated on lower shoulder 46' of cover 22', is larger than the outside diameter of fish 48'. When overshot A is used to retrieve fish 48', outer cover 22' is lowered over fish 48' as shown in FIG. 15. As further seen in FIG. 16, further displacement of overshot A causes collet heads 38' to come into contact with fish 48', causing the upward displacement of collet heads 38' along surface 40'. As collet heads 38' are pushed upwardly along surface 40', spring 16' is compressed and variable volume cavity 34' increases in volume.
During the further upward movement of collet 20' along mandrel 12', collet heads 38' then slide up inclined ramp 42'. Collet heads 38' are cammed towards vertical large diameter surface 44' by fish 48' after sliding up inclined ramp 42'. At this point, the internal diameter of collet heads 38' is greater than the external diameter of fish 48', so further axial movement of overshot onto fish 48' causes collet heads 38' to surround fish 48'.
When collet heads 38' are adjacent internal groove 50' in fish 48' (FIG. 17), the direction of overshot movement is reversed. This causes collet heads 38' to slide down inclined ramp 42'. As they do so, collet heads 38' are pushed radially inwardly into external groove 50'. Overshot A is further raised until collet heads 38' rest on top of lower shoulder 46' (FIG. 18). Collet heads 38' are then locked into external groove 50' and fish 48' can be raised.
As with the first prior art embodiment, overshot A requires an initial collision between collet heads 38' and fish 48' in order to push collet heads 38' up surface 40' and along inclined surface 42'. The repeated collisions and buckling forces sustained by collet ring 20' weakens fingers 36'.
These and other disadvantages of the fishing spear and overshot of the '201 patent are addressed by the improved fishing spear and overshot/external pulling tool of the claimed invention.